1. Field of the Invention
The present invention relates to a method and arrangement for time-division multiplex transmission of data, in digital form, in a bus system, with varying signals, such as digitalized analog signals, stochastically or randomly occurring switching signals, etc., being possible; the bus system comprises a central control unit, several equivalent participating or subscribing stations which are subordinate to the central control unit, and at least one bus line or data bus, which connects all of the subscribers.
2. Description of the Prior Art
With time-division multiplex transmission of digital communication or information signals via a common data transmission medium, there is a fixed agreement via the allocation of the transmission times (time slots). Different methods are known for trying to resolve the problem of regulating the bus access; these methods are divided into centralized and decentralized approaches. The centralized approaches operate with an overriding control unit, which respectively assures bus access to a bus subscriber. With the decentralized methods, a process which takes place within a given subscriber ensures that only one subscriber at a time can engage the bus. The decentralized methods have the advantage that they require no central control unit. For this reason, however, it takes a relatively long period of time until a subscriber can obtain bus access. Under certain circumstances the method jams itself, for example the so-called CSMA/CD method (CSMA/CD=Carrier Sense multiple Access with Collision Detect). Some methods are rather problematical for subscribers of different signal classes, and when a subscriber fails (token-passing method, but also CSMA/CD methods).
The centralized methods have the advantage of being able to monitor and control the subscriber in a very precise and comprehensive manner. However, they load the transmission medium by additional data exchange for organization purposes.
German Patent No. 22 62 933 Hilderbrand et al dated Jan. 7, 1982 discloses a method of time slot allocation which can be used both centrally and decentrally. In this method, no rigid limits exist in the transmission capacity which is available for the individual signal classes. Instead, a flexible adaptation to the traffic is effected, with the possibility of totally utilizing the system capacity. Therefore, with this system, to transmit different types of information signals in a time-division multiplex transmission system, where the time multiplex frames are divided into m subframes, and each subframe is divided into n time slots, there is provided that this loading of the time multiplex frame be effected by signals in such a way that initially in each case the i.sup.th time slot of the subframe is loaded, and only after all of the subframes of a time multiplex frame of the i.sup.th time slot are occupied, is an adjacent time slot of the subframe additionally loaded.
However, the drawback to this heretofore known method is that when the system capacity is fully utilized, access to the transmission medium for data transmissions which become additionally required is blocked.
An object of the present invention accordingly is to provide a method and arrangement of the aforementioned general type which optimally controls the bus access while taking into consideration the available bandwidth, which during overload does not block the data traffic, which permits rapid access to the transmission medium and which is flexible with regard to the choice of transmission medium as well as in the design of the bus system.